1. Field of the Invention
This invention relates to an optical fiber cable which is lightweight and flexible and has a high strength.
2. Prior Art
It has been desired that an optical fiber cable has a smaller diameter and a high strength and is lightweight and flexible. One example of the conventional optical fiber cable comprises an elongated tension member or core made of twisted steel wires, a plurality of optical fibers spirally wound around the tension member, a cushioning member wound around the spirally-wound optical fibers, a holder tape of a plastics material applied around the cushioning member, and a sheath wound around the holder tape. This conventional optical fiber cable is advantageous in that it can has a small diameter. However, it has a relatively low mechanical strength, and besides it is relatively heavy in weight because of the use of the tension member of steel wires.
Another conventional optical fiber cable comprises an elongated body or spacer member made of polyethylene or the like having a plurality of spiral grooves formed in a circumferential surface thereof and extending longitudinally thereof, optical fibers received respectively in some of the spiral grooves, tension wires of steel received respectively in the other grooves, a cushioning member wound around the body, a holder tape of a plastics material applied around the cushioning member, and a sheath wound around the holder tape (Japanese utility Patent Application No. 57-192058 of Ishida et al.). Although this conventional optical fiber cable has an increased strength, it is relatively heavy in weight on account of he use of the steel tension wires and is inferior in flexibility.